can only be used once per container

[jhesqqq]

version:4.4.13
Q:
What I want to implement is that there is also Pattern and Input help_heading under the Usage help_heading in the cli interface, so that my Pattern and Input parameters are grouped together.
But an error was reported, which said that can only be used once per container.
How can I derive multiple subcommands?
I have noticed that there is a subcommands method, whether this can solve this problem, and if so, please give an example.
Thank you.

/// a demo for clap
#[derive(Parser, Debug)]
#[command(version = "1.0", author = "test")]
pub(crate) struct Command {
    #[clap(subcommand)]
    pattern: Pattern,
    #[clap(subcommand)]
     input: Input,
}

[epage]

A more complete demo code with expected output would help in understanding what you are trying to do.

We only support on #[command(subcommand)] to exist because subcommands are mutually exclusive; they best exist within an enum. You can flatten an enum of subcommands into an enum of subcommands. If this is to get different headings for each group of subcommands, that is not supported at this time. See #1553.

[jhesqqq]

Thank you for your answer.
I also have a question about whether I can assign a name to the parameter group.
Like Input and Probe under Flags in this picture.
How do I implement it, either derive or build.

[epage]

That is the help_heading feature and it works in both APIs.

[jhesqqq]

Thank you very much for your answer, my problem has been solved.
clap is very strong, but I have one regret.
short can only be entered as a single char, I searched for related questions such as #5180.
I don't think two char is too wide, like the picture I posted earlier.
A mere 26 characters is often not enough for a cli tool.
I think clap would be even more perfect if it could achieve longer characters.

[epage]

Is there a reason to do that as a short, rather than as an alias for a long?

[jhesqqq]

If I only use long, then I need to use two -- in my argument, when I actually want to use one - to implement my command input.
If I mixed short and long, using some of them and some of them all, the command-line pages would be very unfriendly to the user.
I think short can be fixed to 1-2 char.
For example, if I want to use status-code argument, when using only long, I need --sc.
If I change it to short, -s is fine, but it will conflict with my other parameters.
But when short allows two characters, I only need -sc, and there is no conflict.

[ethanmsl]

Hey jhesqqq

One of the great things about CLIs is that they can be very quick and efficient, and this is partly because they have some norms that let people make guesses about their behavior and remember commands more easily.

Short-flags also typically enjoy combo behavior. And clap implements that automatically.
e.g. ls --list --all == ls -l -a == ls -la
Even if we ignored people expecting single char short-flags as an interface the combo behavior would be more than ungainly to read.

(There are a lot of things that are good ideas in isolation, but become much more awkward in contexts with established norms. Interfaces are probably prominent among example classes.)

Here's a quick mod of one of clap's examples to show the behavior in clap btw.
No special code to achieve this, it's just clap being great and helping us match use expectations.

/// Simple program to greet a person
#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
struct Args {

        /// Name of the person to greet
        #[arg(short, long)]
        name: String,

        /// Number of times to greet
        #[arg(short, long, default_value_t = 1)]
        repeats: u8,

        #[arg(short, long, default_value_t = false)]
        party: bool,

        #[arg(short, long, default_value_t = false)]
        colors: bool,
}

[jhesqqq]

Thank you for your answer.
I didn't think to use composite behavior, which makes short's restriction necessary.
This gave me a taste of the power of clap, and I'm sure I'll be using this behavior in the near future.
As a suggestion, I would like to add a global feature to disable the combined behavior for multiple situations.
When we disable this line, short can become two or more characters.
When you can't help using this line (enabled by default), short is just a single character and takes advantage of the combination.
Hopefully clap gets stronger and stronger